This disclosure relates generally to semiconductor processing and more particularly to methods for guiding current in light-emitting diode (LED) devices.
During the fabrication of light-emitting diodes (LEDs), an epitaxial structure of an “LED stack” including layers of p-doped GaN and n-doped GaN, for example, may be formed. FIG. 1 illustrates such an example of a conventional LED device 102, having an n-doped layer 106 and a p-doped layer 110 separated by a multi-quantum well (MQW) layer 108. The device 102 is typically deposited on a carrier/growth-supporting substrate (not shown) of suitable material, such as c-plane silicon carbide (SiC) or c-plane sapphire, and bonded via a bonding layer 204 to a thermally and electrically conductive substrate 101. A reflective layer 202 may enhance brightness. Voltage may be applied between the n-doped layer 106 and p-doped layer 110 via an n-electrode 117 and the conductive substrate 101, respectively.
In some cases, it may be desirable to control the amount of current through the n-electrode 117 to the substrate 101, for example, to limit power consumption and/or prevent damage to the device 102. Therefore, an electrically insulative layer 206 may be formed below the p-doped layer 110, in the reflective layer 202, to increase contact resistance below the n-electrode 117 and block current. The insulative layer 206 may be similar to the current-blocking layer described in Photonics Spectra, December 1991, pp. 64-66 by H. Kaplan. In U.S. Pat. No. 5,376,580, entitled “Wafer Bonding of Light Emitting Diode Layers,” Kish et al. teach etching a patterned semiconductor wafer to form a depression and bonding the wafer to a separate LED structure such that the depression creates a cavity in the combined structure. When the combined structure is forward biased by applying voltage, current will flow in the LED structure, but no current will flow through the cavity or to the region directly beneath the cavity since air is an electrical insulator. Thus, the air cavity acts as another type of current-blocking structure.
Unfortunately, these approaches to current guiding have a number of disadvantages. For example, the electrically insulative layer 206, the air cavity, and other conventional current-blocking structures may limit thermal conductivity, which may increase operating temperature and compromise device reliability and/or lifetime.
Furthermore, a conventional LED device, such as the device 102 of FIG. 1, may be susceptible to damage from electrostatic discharge (ESD) and other high voltage transients. ESD spikes may occur, for example, during handling of the device whether in fabrication of the LED device itself, in shipping, or in placement on a printed circuit board (PCB) or other suitable mounting surface for electrical connection. Overvoltage transients may occur during electrical operation of the LED device. Such high voltage transients may damage the semiconductor layers of the device and may even lead to device failure, thereby decreasing the lifetime and the reliability of LED devices.
Accordingly improved methods for guiding current through an LED device are needed.